The present invention relates generally to internal combustion engines. More particularly, the present invention relates to two-stroke, diesel aircraft engines.
Internal combustion engines generally include an engine block defining a cylinder which includes a reciprocally operating piston. A cylinder head is generally mounted to the engine block over the cylinder. As generally known, the overall operation, reliability and durability of internal combustion engines depends on a number of design characteristics. One such design characteristic involves the piston pin or wrist pin/connecting rod connection. Uneven wear, excessive deflection or other structural deformities of the wrist pin will adversely affect the performance of an engine. Another design characteristic involves providing adequate cooling for fuel injectors. Generally, fuel injectors are in close proximity to the high heat regions of the combustion chambers. Without proper cooling, a fuel injector can malfunction and, in some cases, completely fail. Another design characteristic involves sufficiently cooling the cylinder heads. Thermal failure or cracking of a cylinder head results in costly repairs to the engine. Yet another design characteristic involves providing coolant to cooling jackets in multiple cylinder engines having a plurality of cylinder banks. Inadequate flow or obstructed flow of the coolant through the cooling jacket can result in engine failure.
A heat conducting fireplate or deck is typically provided beneath the cylinder head, and a combustion chamber is defined between the piston and the fireplate. Many internal combustion engines utilize a plurality of head bolts to secure the cylinder head to the engine block so as to provide a clamping force that seals the cylinder head to the engine block to prevent the undesirable escape of by products created by combustion within the combustion chamber.
The present invention provides an internal combustion engine having many advantages over prior art engines. In particular, the present invention provides certain improvements that are particularly well suited for use in two-stroke, diesel aircraft engines. The invention includes a new wrist pin/connecting rod connection, a new cooling system for fuel injectors, a new cylinder head cooling arrangement, a new cooling jacket cross-feed arrangement, and a new combustion seal arrangement.
The wrist pin, especially in two-stroke diesel engines, is nearly continuously under load. It is not uncommon for wrist pins to deflect under heavy or continuous loads. A heavy or thick walled wrist pin reduces the deflection, but at the cost of a substantial increase in weight. Thus, there is a need for a new wrist pin/connecting rod assembly which makes it less likely that the wrist pin will deflect under heavy or continuous loads, yet which does not appreciably add to the overall weight of the engine.
Providing a wrist pin/connecting rod assembly in which the wear on the bearing surface of the wrist pin is evenly distributed is difficult at best. Uneven wear of the wrist pin bearing surface can result in poor engine performance. Thus, there is a need for a wrist pin/connecting rod assembly which minimizes uneven wear on the wrist pin bearing surface.
Accordingly, the invention provides a connecting rod with a cradle-like upper end. In other words, the upper end of the connecting rod has an arcuate portion and does not encircle the wrist pin. The wrist pin has an outer surface in engagement with the arcuate portion of the connecting rod, and a plurality of fasteners (e.g., screws) secure the wrist pin to the arcuate portion of the connecting rod by extending through the wall of the wrist pin and into an insert within the wrist pin. Because the arcuate portion of the connecting rod does not completely encircle the wrist pin, the entire xe2x80x9ctopxe2x80x9d of the wrist pin (the side of the wrist pin farthest from the crankshaft and nearest the piston crown) can bear against the piston. In other words, a longitudinal portion of the wrist pin that does not engage the arcuate portion of the connecting rod can bear against the piston. This results in the load and the wear being more evenly distributed across substantially the entire longitudinal length of the wrist pin and, therefore, a lighter wrist pin than would otherwise be necessary can be used. Moreover, the wrist pin insert stiffens the wrist pin, also allowing the use of a thinner wrist pin. In addition, because the wrist pin cannot pivot relative to the connecting rod, the forced movement or rocking of the wrist pin as the connecting rod pivots during operation of the engine aids in oiling and minimizes uneven wear on the wrist pin bearing surface.
Fuel injectors are subject to intense thermal conditions because of their general proximity to the cylinder heads. One way to cool fuel injectors is to install the fuel injectors through cooling jackets which are adjacent the cylinder heads. The cooling jackets can cool both the cylinder heads and the fuel injectors. However, cooling jackets are not always sufficient to cool the fuel injectors. Moreover, in some engine designs, cooling jackets are not located in positions which allow them to be used to cool the fuel injectors. Thus, there is a need for a new fuel injector cooling system which enhances operation of or operates independent from a cooling jacket.
Fuel pumps generally deliver more fuel than the fuel injection system and engine can utilize at any given moment. As a result, the excess fuel is typically returned to a fuel supply tank for further use. Rather than returning the overflow fuel from the fuel pump directly to the fuel supply tank, the present invention utilizes the overflow fuel to cool the fuel injectors. Circulating the overflow or bypass fuel from the fuel pump through the fuel injectors for the purpose of cooling the fuel injectors makes use of an existing liquid flow not previously used to cool the fuel injectors. The overflow fuel flows into each fuel injector via a newly-provided inlet port and flows out through the known leak-off port. It is not uncommon for engine coolant in a cooling jacket to reach temperatures in excess of 240xc2x0 F. The overflow fuel is significantly cooler than the engine coolant running through the cooling jacket, thereby providing an improved method of cooling the fuel injector to increase fuel injector life. In those engines which do not use a cooling jacket, the fuel injector cooling system of the present invention provides a new way of cooling the fuel injectors.
Accordingly, the invention also provides a fuel injection system having a fuel injector for injecting fuel into a combustion chamber. The fuel injector includes a fuel inlet port, a fuel outlet port and a fuel passage communicating between the fuel inlet port and the fuel outlet port. The fuel injector further includes a cooling fuel inlet port, a leak-off fuel outlet port and a cooling fuel passage communicating between the cooling fuel inlet port and leak-off fuel outlet port. The fuel injection system includes a bypass fuel line which communicates between a fuel pump and the cooling fuel inlet port of the fuel injector. Overflow fuel from the fuel pump flows through the bypass fuel line and through the fuel injector to cool the fuel injector. Using the excess fuel from the fuel pump to cool the fuel injector simplifies or supplants the cooling jacket.
A problem particularly prevalent with aircraft engines concerns ice build-up on the fuel filter due to cold outside temperatures. The overflow fuel which cools the fuel injectors is warmed as it flows through the fuel injectors. The warmed overflow fuel is recirculated through the fuel injection system to travel through the fuel filter so as to provide the additional benefit of resisting ice build-up on the fuel filter in cold weather.
Radiant and conductive heating of a cylinder head can raise the temperature of the cylinder head above its metallurgical and structural limits. Traditionally, cylinder heads are bolted or otherwise secured to the cylinder block or engine block with a suitable head gasket therebetween to effectively seal the cylinder heads and provide the cooling means for the cylinder head. According to a preferred embodiment of the present invention, the cylinder head threads into the engine block. Because of this, cooling passages normally provided between the engine block and the cylinder head cannot be utilized. Thus, there is a need for a cylinder head cooling arrangement which is not dependent on the location of the cylinder head with respect to the engine block, as is the case with prior engine designs.
Accordingly, in another aspect of the present invention, a cooling cap is mounted on the cylinder head. The cooling cap and the cylinder head combine to define a substantially annular cooling passageway. The cooling cap further includes inlet and outlet ports which communicate with the cooling passageway, so that cooling fluid can flow through the cooling passageway to cool the cylinder head. According to one aspect of the present invention, the inlet and outlet ports of the cooling cap communicate with the cooling passageway, so that the cooling fluid is caused to flow from the inlet port, substantially all the way around the cooling passageway, and then out the outlet port to provide enhanced cooling effectiveness. The cooling cap is adjustably positionable on the cylinder head, such that the inlet and outlet ports of the cooling cap can be properly aligned with ports in the engine block. In other words, the cooling cap is connectable to a cooling jacket in the engine block regardless of the position of the cylinder head with respect to the cylinder block or engine block. Because the cylinder head threads into the engine block, it is not known exactly where the cylinder head will be positioned in terms of the engine block. Thus, the adjustable cooling cap of the present invention is especially advantageous in an engine in which the cylinder head threads into the engine block.
Threading the cylinder head into the engine block according to the present invention provides the added benefit of eliminating the bolt and head gasket system of prior engines. This eliminates a possible point of failure, while at the same time reducing the number of parts to assemble the engine. According to one aspect of the present invention, the engine block includes female threads concentric with the cylinder and the cylinder head includes male threads which engage the female threads on the engine block. Because the traditional bolt and head gasket assembly can be eliminated, in order to provide a proper combustion seal, the present invention provides, according to one aspect thereof, a biasing spring between a cylinder head and a fireplate. The spring provides a downward force against the fireplate to offset an upward force created by combustion within the combustion chamber, thereby substantially ensuring that a proper cylinder head combustion seal is maintained.
In V-type engines, a cooling jacket and an associated thermostat are typically provided for each cylinder bank. A problem with such prior arrangements is that if one thermostat fails, there is no mechanism to allow cooling fluid to flow through the associated cooling jacket. Another problem with such prior designs is that the temperature gradient between the hot cylinder heads and the cooler lower crankcase can be significant, thereby adding undesirable stress to the engine block and other engine components. Thus, there is a need for a new system which provides redundancy of thermostat operation and thermal coupling between the cylinder heads and the lower portion of the engine.
Accordingly, the invention also provides a cross-feed cooling passageway in the engine block of a V-type engine. The cooling passageway extends between a first cooling jacket adjacent a first cylinder bank and a second cooling jacket adjacent a second cylinder bank. A first thermostat communicates with the first cooling jacket and a second thermostat communicates with the second cooling jacket. The cooling passageway provides cooling fluid flow between the cooling jackets. This is particularly advantageous in the event that one of the thermostats fails. The cross-feed passageway will allow the cooling fluid to continue to flow if one thermostat fails, so as to reduce the possibility of damage to the engine from over-heating. Another advantage of the cooling passageway is that it reduces the temperature gradient between the cylinder heads and the lower crankcase.